The abandonment of non-producing or uneconomic oil or gas wells presents a number of safety and environment issues. Typically, in the abandonment process, all production and surface wellbore casings along with conductor barrels and cement liners have to be removed to a depth of two meters below the surface.
A previous method for such removal required a large scale excavation of soil from around the existing wellbore. In order to do this, line location companies needed to be brought in to determine locations of any existing oil, gas and/or utility lines. Proper safety practices typically require that a very large area be excavated to allow a welder and an assistant to descend into the area to the required depth to cut the existing steel casings and cement liners. This cutting of the casing is done using a cutting torch.
Typically, the casing is cut horizontally and then vertically to remove the outer layer. Any cement present then has to be removed using either a jackhammer or sledge hammer. This allows access to secondary steel casings that are cut using the cutting torch again.
Throughout this process, a source of ignition, the cutting torch, is being used in an area wherein there is a possibility for the presence of explosive or flammable gases or liquids. This type of work environment may be referred to as a hot work area. A significant safety threat is inherent for the personnel in a hot work area and is further exasperated through the used of a cutting torch or any other heat based cutting tool.
One previous attempt at overcoming this issue was to provide a different type of tool consisting of metal blades that would be lowered inside the casing and then rotated and expanded to cut through the casing. Such a tool is described in U.S. Patent 5,685,078. Some problems associate with this tool and this method of cutting are that if there is an movement of the casing while being cut, the tool becomes jammed inside the casing. In addition, being a metal on metal cut, there is still the possibility of sparking which can ignite any explosive or flammable gas or fluid and can also cause a heat build-up which may ignite any explosive or flammable gas or fluid in the hot work area. Further, the tool can only cut only layer at a time and has to be removed and set to a different cutting depth for each cut. Finally, this type of tool does not cut well or sometime at all, though cement.
There is therefore a need to provide a cutting tool that overcomes one or more of the shortcomings of the current cutting tools or methods outlined above and/or observed in the field.